2 APT 26 Years Supplying Surge Protective Devices ISO Quality Management SystemISO evaluation by ULPower Quality Assurance magazine –PQ 50 CompanyFrost & Sullivan ranked APT –Leading Supplier of Three Phase DevicesMarket Engineering Customer Focus AwardsMembers of UL, IEEE, NEMA standards committeesPQ50 - Handout #1 in your binder.
3 What Is a Surge/Transient? High amplitude, short duration overvoltageCan be positive or negative polarityTidbit: Transient: > two times system’s RMS voltageNoise: < two times system’s RMS voltageTransient Overvoltage – Can be thousands of voltsWhat is a transient? By IEEE definition, a transient is at least two times the system’s RMS voltage. This contrast noise which is less than two times the system’s RMS voltage. A transient is a very short duration event (microseconds) and will be a significant overvoltage or impulse on the AC sine wave. A transient is a small fraction of a 360° sine wave.Millionths of second33
4 What Causes Surges/Transients? LightningSwitching:Load Switching – utility & customerMotors, Large Loads, Faults, Fuse OperationSource SwitchingSmart Grid, Gensets, PV, Wind TurbineInternally generated surges: ≈70%Externally generated surges: ≈30%Transients tend to be caused by lightning, utility operations or internal disturbances.There are two predominant wave forms used to describe transients. One is a high-energy impulse, a rapid rise and fall. The other is a ring wave, which oscillates at high frequency as it dissipates.IEEE has developed typical waveforms to describe these events, which will be discussed later.In outdoor environment, this ratio probably reverses44
5 Effects of Transient Voltages? Microelectronics Intolerant to SurgesDisruptionLockups, Downtime & Interruption costsComputing glitches and errorsDegradationMicroelectronicsSlow & continuous damage to motor insulationDestructionFailed microelectronics, ballasts,motors, controllers, etc.Maybe analogous to:‘Water hammer’ in a plumbing system‘Rust’ to microelectronicsHow do transients cause damage? Transients can cause data transfer glitches as "0's"are misinterpreted as "1's" in a digital data transmission. Bad data can and has shut down operations. The overall cost of any kind of disruption is staggering. Manpower is expensive as people stand around waiting for equipment to reset. Production is lost in batch runs. Many industries require a continuous production flow or else the product must be discarded.Transients have a cumulative effect much like static discharges. One of the fundamental purposes of surge suppression is to limit voltages to microelectronic equipment such as IC chips. Chips are composed of layered silicon substrates that are permanently damaged when excessive voltage “punches-through” a silicon layer. This occurs at the micron level and is difficult to troubleshoot. The appropriate repair is to replace suspect components.A rare but worst case transient scenario is substantial destruction. This is usually caused when a component fails due to a transient and an unusual chain of events leads to catastrophic failure.5
6 MOV - Metal Oxide Varistor Varistor - variable resistorSemiconductor; generally zinc oxideConnects parallel to load (not series)Thickness determines clamping voltageDiameter determines current capacityMOV symbolThe Metal Oxide Varistor is the primary surge suppression component. MOVs are typically made of zinc oxide and are a solid-state semiconductor device. They are bi-directional and will control both positive and negative surges. MOVs come in many diameters and configurations. They are very common in automotive applications.6
7 MOV - Metal Oxide Varistor MOV seeks to equalize overvoltageVoltage sensitive conductor: V = IR & I = V/RAt ‘low’ voltages: very high impedance, 109: I 0AAbove ‘threshold’ voltage: resistance approaches 0: I = high ACurrent diverts through MOV as I = V/R (high V, low R)Normal voltageOvervoltageV VV VI == 0.12AI == 6000AR R The Metal Oxide Varistor is the primary surge suppression component. MOVs are typically made of zinc oxide and are a solid-state semiconductor device. They are bi-directional and will control both positive and negative surges. MOVs come in many diameters and configurations. They are very common in automotive applications.Trivial leakage currentSurge Current
8 MOV - Metal Oxide Varistor Overvoltage diverts through MOV as currentVoltage is “clamped” or “equalized” as energy is transferred to other side of MOV(s)MOV does not ‘absorb’ surge, however, I2R heat is retainedBidirectional – Operates same for positive or negative surgesCreates a momentary low impedance (acting like short-circuit) to pass transient energy to earth; analogous to water heater pressure relief valve-MOV reaction times are less than 1/2 nanosecond… transients occur in the microsecond range of time.MOVs sum like capacitors when installed in parallel. Resistance decreases like paralleled resistors.Paralleling MOVs increases capacity, lowering impedance at the same time.++-
9 SPD Operation Load 1 Load 2 Load 3 MOV/SPD Acts as a momentary ‘short circuit’ ‘short circuit’ ≈ no overvoltage ≈ protected loadAfter the surge, MOV/SPD automatically resets itself to high impedance state drawing no currentLayman’s Terms: Visualize an ‘electronic guillotine’ that chops the head off a surge and sends it away
10 ‘short circuit’ ≈ no overvoltage ≈ protected load SPD OperationLoad 1Load 2Load 3MOV/SPD Acts as a momentary ‘short circuit’, then resets itself after the surge‘short circuit’ ≈ no overvoltage ≈ protected load10
11 SPD Connector Leads Need short lead lengths! NEC : “The conductors used to connect the SPD (surge arrester or TVSS) to the line or bus and to ground shall not be any longer than necessary and shall avoid unnecessary bends”Industry typically states: Each foot of conductor adds V to clamping voltageNo Sharp bends or kinksNo Wire Nuts!Right Hand Rule – can cancel inductive effects by bundling, tie-wrapping conductors together
14 APT Here to Help: (800) 237-4567 Specification Assistance Training Sounding Board for issuesCompetitive crosses or analysisGeneral HelpOn-Line webinar servicesForensic Testing & Analysis of failed SPDsEtc.
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